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Why were prehistoric insects so huge?

Do you complain about dead bugs on your windshield? Well, be thankful that insects today are considerably smaller than some of their prehistoric ancestors.

Do you complain about dead bugs on your windshield? Well, be thankful that insects today are considerably smaller than some of their prehistoric ancestors.

OK .. they were never quite this big!

You have to use your imagination to picture these creatures – straight from a horror movie. There were 9-foot long millipede-like monsters, and dragonflies with wingspans of nearly two and a half feet.

But why didn’t these giant insects survive to present times?

There are two main reasons. One is that our atmosphere has changed. When the giant insects were around – 350-50 million years ago – during Earth’s Carboniferous and early Permian period – our planet was warmer, moister, and contained more oxygen. Back then, the atmosphere contained over 30 percent oxygen, compared to today’s air, which is made up of 21 percent oxygen

Oxygen levels are especially important for insects because they don’t have lungs. Instead, they rely on air flowing through a series of opening across their bodies called spiracles, that connect directly to the tissues that need oxygen.

Another important player in the decline of gigantic bug populations was the evolution of birds.

About 150 million years ago, the oldest known bird – Archaeopteryx – appeared. Over time, birds evolved to be faster and more agile than the giant insects.

Though we associate giant bugs with the distant past, some of today’s insects are actually larger than their ancestors.

Luckily for us, most insects are still small enough to fit under a cup or be swatted by a rolled up newspaper or eaten by a bird.